Cost-effective core@shell structured zero-valent iron nanoparticles @ magnetic (nZVI@Fe3O4) for Cr(vi) removal from aqueous solutions: preparation by disproportionation of Fe(ii)

Abstract

Nanoscale zero-valent iron (nZVI) and its composites are known for their excellent ability to remove Cr(VI), but their preparation can be expensive due to the reduction processes. This study presents a cost-effective method to prepare core@shell structured nZVI@Fe₃O₄ nanocomposites using a novel Fe(II) disproportionation reaction. The nZVI@Fe₃O₄ was thoroughly characterized using various techniques, including FESEM, HRTEM, EDS, XPS, XRD, FTIR, and VSM. Batch experiments were performed to evaluate the removal efficiency of nZVI@Fe₃O₄ in eliminating Cr(VI) ions from aqueous solutions, while classical models were employed to investigate the influencing factors associated with the removal process. The results showed that a 0.7 mg per ml NaOH solution reacted with Fe(II) at 150 °C for 0.5 h could be used to prepare nZVI@Fe₃O₄ composites efficiently and inexpensively. nZVI@Fe₃O₄ was able to remove more than 99% of Cr(VI) from both simulated Cr(VI) solutions and real electroplating wastewater, and the recovery and preparation could be easily performed using external magnets to separate it from the solution. At pH 6.0, the maximum adsorption capacity (q_max) for Cr(VI) reached 58.67 mg g⁻¹. The reaction mechanism was discussed from the perspective of electron transfer. Overall, the results suggest that nZVI@Fe₃O₄, an efficient adsorbent prepared using an environmentally friendly and inexpensive Fe(II) disproportionation reaction, is a promising option for the treatment of Cr(VI) from industrial wastewater and other contaminated water sources.